This is often referred to as CMYK where K stands for black. In theory, solid overlapping layers of C, M, and Y ink produce black. In reality the outcome is dirty brown unless mixed exactly evenly so the black ink replaces the other three layers. See under color removal.
In the RGB color space the colors are added, thus you start with levels of dark colors which are added to produce lighter colors. RYB uses pigments, which are not added, and thus combining colors using the RYB color system will result in a darker color.
